Knurled piercing punch



March 8, 1960 w. G. PORTER 2,927,492 KNURLED PIERCING PUNCH Filed Feb. 29. 1956 'I i'll mmm III I ATTgA/EYS.

United States Patent O KNURLED PIERCING PUNCH Walter G. Porter, Cncinati, Ohio Application February 29, 1956, Serial No. 568,475

2 Claims. (Cl. 83-698) This invention relates to punches used in punch and die sets for piercing multiple holes in materials such as metal sheets and plates.

One of the primary objects of the invention has been to provide a knurled punch which may he driven in a simple manner into its mounting hole, thereby eliminating'much of the precise machining and fitting usually associated with die setting practice. The improved punch is intended primarily to reduce the cost of die sets and to make it possible to assemble them rapidly as needed for various hole patterns.

In general, the ordinary multiple hole die set comprises a punch plate for mounting the punches, a die plate for supporting the work, and stripper means for holding the work upon the die plate as the punches are withdrawn from the Work after piercing it. The punches must be located in precise registry With matching die apertures in the die plate, such that the ends of the punches penetrate the work and pass into the die apertures without interference. Upon each stroke, the punches simultaneously form the pattern of holes and discharge the sheared slugs through the die apertures. The repeated punching impacts have a tendency to loosen the punches in the punch plate, leading to interference with the die holes and resulting in punch breakage or improper operation.

A number of different ways of locking or setting the punch in its plate or holder have been developed in the past. For example, conventional punches may be provided with an enlarged head for locking them in the punch plate or they may he secured by set screws or other clamping means. However, in all cases, to properly mount the conventional punches, requires several machining operations and involves considerahle time and die v setting expense.

According to the present invention, a serrated or knurled section is formed on the shank or body portion of the punch to provide a self-locking action as the punch is driven into the mounting hole of the punch plate. The serrations, which form the knurled section, preferably consist of ridges spiralng lengthwise of the shank of the punch in the form of self-tapping screw threads or rifling. The *diameter of the knurled section is greater than the diameter of the shank, the relationship being such that the shank provides a push fit or a light press fit with the hole of the mounting plate and serves as a guide or pilot for the knurled section. The punch plate is made of metal which is somewhat softer than the punch to allow the spiral serrations'to as the punch is pressed home.

To install the punches, they are simply inserted, into the mounting holes of the punch plate, the shank is pushed through the mounting hole under light pressure, then heavy pressure is applied to the punch to force the knurled section into the hole. As the serrations are forced in, their leading ends cut their way and create a rifling action which imparts rotary motion to the shank. This rotary motion aids the shank in piloting the knurled section and improves the fit of 'the shank inthe hole.

cut the threads ece When fully inserted, the leading ends of the serrations form minute abutnents embracing the uncut portion of the hole surrounding the shank. The abutment action, combined with the spiral formation of the serrations, locks the punch rigidly in the plate against endwise withdrawal.

In the typical punch and die installation, the punch plate is mounted upon the ram of the press, usuallywith a hacking plate between the punch plate and ram. The upper ends of the punches must be fiush with the upper surface of the punch plate so that the compressive force of the punches reacts directly against the hacking plate.

The present punch is intended to be mounted in this manner and presents the following particular advantages over conventional punches. In the first place, the drive fit allows the upper end of the punch to be driven-fiush with the surface of the punch plate whereas the conventional punches usually require the top surface to be ground or machined fiush to seat properly against the hacking plate. Secondly, the shank and serrated section" creates a rigid mounting, taking advantage of the full thickness ef the punch plate to reduce punch hreakage due to looseness and misalignmen Briefly therefore, the elimination of machine work saves" considerable time in constructing the die set for `a required hole pattern and reduces greatly the over-all cost of a given job. On the other hand, the full length press fit causes the punch to perform better than precisely" fitted conventional punches of comparable size.

The various advantages of the invention are brought out in greater detail in the following description in conjunction with the drawings. 4

In the drawings:

Figure 1 is a fragmentary cross sectional view of a die set showing a typical installation of the improved punch, the structure being shown in its open position with the work piece resting upon the die plate.

Figure 2 is a view similar to Figure l showing the' punching stroke.

Figure 3 is an enlarged fragmentary view showing the punch partally driven into the punch plate at initial installation.

Figure 4 is a View similar to Figure 3, showing the punch completely installed.

Figure 5 is an enlarged side view of the-punchgfur ther illustrating its Construction.

Figure 6 is an end View of the head section of the punch illustrating the preferred profile of the serrations.

'Referring to Figure l, the knurled punch is shown in mounted position relative to the ram 10 of a die press,

the die plate 11 being mounted upon the stationary platen 12 of the press. The knurled punch, which is indicated generally at 13, is fitted into the punch plate 14, a backup plate 15 being interposed between the punch and ram.

The die plate 11 is provided with the die hole 16 aligned with the axis of thepunch, such that the piercing 'nib v 17 of the punch passes through the work 18 and into' the punch plate. During the return stroke, the stripper expands, thus holding the work upon the die plate as the piercing nib of the punch is withdrawn from the punched hole. i

The die set shown in the drawings represents a low 'cost unit for-limited producton asnoted with-reference tothe' aircraft industry. However, it will be understood that the improved punch is also intended' to be used in the more elaborate die sets designed for mass production Operations. In this event, the die setspreferably is provided with the conventional spring loaded stripper plate which is wellknown in the industry. It will be understood that in any case, the die set is provided with the usual guide pins or other Components to. hold the punch plate and die plate in alignment during the working stroke.

*Inconstructing the die set shown in the drawings the hole centers are accurately located at the required' centers, utilizing a suitable template or jig boring machine. To save time, the punch plate and dic plate may be clamped together with the guide pins in place so that matching sets of holes may be drilled at. the same time through both'plates. Thereafter, the punch holes may be finished to the required diameter, as governed by the diameter of th'epunch shani( 22 to provide the required precision fit with the shank. The punch is then inserted in each hole and pressed or driven in until the knurled upper section 23 cuts its way into the bore with itsupper end flush with the top surface of theplate'as shown in Figure 4.

As viewed in' Figure 6, the serrations 24 of the knurled section preferably are in the form of V-shaped ridges, generally similar to the profile of a ?screw thread. The serrations extend g'enerally lengthwise but at a, slight angle to the nxis of the shank in slightly spiral formation. The serrations may be tormed by a knurling oper- 'ati'onbefore the punch is hardened so that the metal is displaced outwardly from the surface of the cylindrical shanklto form the. ridges. By way of example the diameter 'ofcthe knurled section 23 may be from ten, to twenty thousandths of an inch greater than the diameter' of shank 22. After the serrations are formed, the punch is hardened and is ready to be mounted in the punch plate 14.

This relationship of diameters may vary in accordance with the size of the punch and other variable factors. In any case, the knurled section is designed to allow the punchto be driven home without unreasonable force and at the same time, to set the punch firmly and maintain accurate alignment for efiicient performance.

It w-illbe understood that in all of the punch sizes, the piercing nib 17 is considerably smaller in diameter than the punch shank 22. This provides a suflicient shank area in hearing engagement withthe punchplate to insure efiicient and' reliable operation under themost adverse working conditions.

Thepunch is mounted in the punch plate simply by insertingtheshank into' the mounting hole and forcing the punchdownwardly until the upper end of the knurled section is flush with the top surface of the plate. This may be-done with a suitable arbor press or with an ordinary machinisfs hammer.

The shank 22 of the punch preferably is ground or otherwise machined to fine finish, related' within fairly ing action tending to reduce surface irregularities in the hole and thereby settles itselfmore securely.

After the knurled section is forced home as shown in Figure 4, the leading erds 25 of the serrations act as minute abutments surrounding the circumference of the uncut section of the hole below the knurled section. The leading ends of the serrations, combined with their spiral formation, create a positive stop which locks the punch rigidly against endwise withdrawal from the punch plate. In addition, the V-shape of the serrations increases the effective hearing, area andi this increaseimproves the gripping effect of the knurled sections.

The punch plate, 'with the several punches mounted in it, is then installed against the hacking-plate and mounted under the ram. In this position', the upper ends of the knurled sections, which are flush with the surface of the plate, seat collectively against the surface of the back-up plate 15, such that the punching impacts travel directly through the punch and; against the back-up plate. As noted earlier, the resistance of the work during the pieroing stroke causes hea y compression forces to build up withinthe punch, Evidently, the forces reach a pealr then the work shears andallows the punch to expard suddenly, thereby tending to explode 'the punch downwa dly from the punch plate. Experience indicates that the present knurled punch will sucessfully operate up to the limits or possibly beyondthe limits of co'nventional punches of' 4 comparable size without developing looseness and misclose tolerances to the diameter of the knurled section.

The mounting hole in the punch plate is accurately machined to provide a pushfit or light press fit with the shank; After the shank is inserted and pushed in under .fairly-light pressure to the position shown in Figure 3,

heavy pressure is applied' to its upper end, causing the leading; 'ends 25 of the se'rations to cut their Way into the hole. This action displaces the metal in the upper portion ofthe hole and cuts the spiral screw threads.

As theknurledsection is -forcedin, rotary motion is imparted to: the punch due to the rifling *action of the spiralserrat-ions; At the sane time, theshank acts as a r alignment under the repeated impacts.

As indicated earler, to obtain satisfactory operation, it is imperative to set the punches precisely in alignment w-iththe die holes of the die plate so that the piercing nibs can enter the die holes without interference. If the punch becomes loose inits mounting plate, then the work will be punched improperly or the punch may break due to striking the surface of the die plate. It will be seen in Figure 4, that thefull thickness of the punch plate is in hearing engagement with the shank and knurled section so as to hold the. punch rigidly againstdefiection of misalignment.

As a matter of contrast, the commonly used head type punch has its head loosely fitted in an enlarged counterbore, with only the shank press fitted in the punch plate. Since the thickness of the head may be as much as onehalf the thickness of the punch plate, the hearing engagement of the headed punch is reduced by that amount. Accordingly, the headed punch must be more accurately fitted, otherwise it is likely to wear under the punching impacts with consequent looseness and breakage during service.

Also as noted earlier, the knurled punch eliminates several of the machining Operations required in meunting a headed punch, such as forming the counter-boxes in the top portion of the die plate and ot grinding the top surface to bring the tops of the heads flush with the top surface of the plate. Since each unit involves a considerable number ot punches, the elirnination collectively of such 1. Punching apparatus adapted to bemounted upon i the ram of a press, said apparatus comprising a punch plate having a pluraiity of cylindrical mounting holes formed therein, a plurality of piercing punches mounted upon said punch' plate, each of said piercing punches being formed of' anetal which is' harder than said punch p ate ch otsaid punches omp ising, a. ylindri al han n said shank being greater in length than the thickness of the punch plate, each of said shanks residing in one of said mounting holes and having an outer end projecting from the side of the mounting plate, a piercing nib projecting axially from said outer end of the shank, said piercing nib having a diameter not greater than one-half the diameter of the shank, and a knurld section on the opposite end portion of said shank, said knurled section being generally cylindrical and extendng to the end of the shank opposite said nib, said knurledsection comprising a series of serrations extending lengthwise of the said shank for a distance substantially less than the thickness of the punch plate, the cross sectionai area of said knurled section being substantiaiiy the same `as the cross sectional area of said shank, said serrationsbeing formed of metal displaced outwardly beyond the periphery of the shank and being embedded in the punch pIate about the mounting hole, said serrations having leading ends providing a series of abutments about the shank and looking the embedded serrations and shank in the mounting hole against outward withdrawal, said shank being snugly fitted in said mounting hole, whereby said shank and the said serrations which are embedded in the plate about the hole together provide a rigid hearing engagement of the punch for the full thickness of the punch plate, the end adjacent the knurled section of each of said punches being disposed substantially flush with one surface of said punch plate.

2. Punching apparatus adapted to be mounted upon the ram of a press, said apparatus comprising a punch plate having a plurality of cylindrical mounting holes formed theren, a plurality of piercing punches mounted upon said punch plate, each of said piercing punches being formed of a metal which is harder than said punch plate, each of said piercing punches comprising a cylindrical shank, said shank being greater in length than the thickness of the punch plate, each of said shanks residing in one of said mounting holes and having an outer end projecting from one side ot the punch plate, a piercing nib projecting axialiy from said outer end of the shank, said piercing nib having a diameter not greater than one-half the diameter of said shank, :and a knurled section on the opposite end portion of said shank, said knurled section being generally cylindrical extending to the end of the shank opposite said nibQsaid knurled section comprsing a series of serrations extending lengthwise of the said shank for a distance less than the thickness of the punch plate, the cross sectional area of said knuried section being substantially the same as the cross sectional area of said shank, said serrations being formed of metal displaced outwardly beyond the periphery of the shank and configurated in spiral formation about the shank, said spiral serrations being embedded in the metal sections of the punch p late about the mounting hole, thereby -locking the shank in the mounting hole against outward withdrawal, said shank providing'a 'pilot bearng embraced by the periphery of the mounting hole and maintairing the outer end of the punch in axial alignment with the mounting hole, whereby said knurled section and said shank provide a rigd hearing engagement of the punch for the full thickness of the punch plate, the end adj acent the knurled section of each of said punches being disposed substartially flush with one -surface of said punch plate.

References Cited in the file of this patent UNITED STATES PATENTS 239,958 Inman Apr. 12, 1881 431,078 Russeli July 1, 1890 1,345,853 Henger July 6, 1920 1,377,799 Brock May 10, 1921 1,482,151 Rosenberg Jan. 29, 1924 1,7 67,492 Valentine June 24, 1930 1,806,434 Wilczek May 19, 1931 2,450,820 Wilcox Oct. 5, 1948 

